1. Field of the Invention
The present invention relates to a quantization method, an image processing apparatus, and a recording medium, and particularly to a quantization technique for converting a continuous-tone image into a binary or multi-level dot image.
2. Description of the Related Art
In the field of printing, a continuous-tone image of a printing subject (for example, an m-level image) is converted to a binary or multi-level dot image (an n-value image) by quantization processing such as dithering and an error diffusion method, where m and n are integers that satisfy 2≦n<m. As a result, an image is formed in accordance with data on the obtained dot image, as is disclosed in Japanese Patent No. 4143560 and “Dithering with blue noise.” by Ulichney, Robert A., Proceedings of the IEEE 76.1(1988): 56-79.
For example, in some inkjet recording apparatuses that form color images, the variety of ink colors is increased to expand the color reproduction region by adding light cyan (LC), light magenta (LM) and special colors to regular ink colors, i.e. cyan (C), magenta (M), yellow (Y), and black (Bk). While a method for increasing the number of ink color variations for use is effective in expanding the color reproduction region, it disadvantageously increases the cost of the apparatus.